1. Field of the Invention
The present invention relates to a semiconductor device manufacturing apparatus and a semiconductor device manufacturing method, and particularly to a diffusion furnace used in a diffusion process and an oxide film forming method using the diffusion furnace.
2. Description of the Related Art
A conventional diffusion furnace and an oxide film forming method using the diffusion furnace will be described. FIG. 1 is a longitudinal-sectional view showing a vertical type diffusion furnace to describe a conventional technique, and FIG. 2 is a diagram showing an oxidation treatment sequence of the conventional diffusion furnace. The vertical type diffusion furnace shown in FIG. 1 includes a furnace tube 2 to which a process gas introducing pipe 5 and a gas discharging pipe 6 are secured, a wafer support boat 3 for mounting wafers 4 thereon, and a heater 1 for keeping the inside of the furnace tube 2 to a desired temperature.
Referring to FIGS. 1 and 2, steps until the oxidation treatment carried out in the vertical type diffusion furnace will be described.
First, wafers 4 are introduced into the furnace tube 2 (first step). At this time, oxygen gas of 2 [SLM] diluted with nitrogen gas of 18 [SLM] is introduced as process gas into the furnace tube 2, and the inside of the furnace tube 2 is kept at 800xc2x0 C. by a heater 1, for example.
Subsequently, temperature stabilization (Recovery) in the furnace tube 2 after the wafers 4 are introduced is promoted (second step), and then the temperature increase to an oxidation treatment temperature, for example, 850xc2x0 C. (Ramp-up) (third step) and the temperature stabilization after the increase of the temperature (Ramp Recovery) (fourth step) are carried out. Here, the gas conditions from the second step to the fourth step are the same as the first step.
In a fifth step, steam gas of 15 [SLM] is supplied as process gas to perform oxidation treatment (Burning), thereby obtaining the final oxide film thickness.
The thickness of the oxide film which has been formed until the time just before the fifth step (oxidation treatment step) is equal to 3.5 nm on the average, and the in-batch film thickness uniformity is equal to 5%. Further, the thickness of the oxide film which has been formed until the time just after the first step is completed is equal to 2.5 nm on the average. The in-batch film thickness uniformity is equal to 8%.
Here, the in-batch film thickness uniformity is defined as a value calculated according to the following equation:
xe2x80x9cin-batch film thickness uniformityxe2x80x9d=(in-batch maximum difference of film thickness average values of respective wafers)xc3x97100/(2xc3x97the in-batch average value of film thickness average values of respective wafers)
Further, the film thickness average value of each wafer represents the average value of film thickness values at five points on the wafer surface (the center point of the wafer and four peripheral points which are located on a cross passing the wafer center point and spaced from the wafer edge by 5 mm).
The thickness of the oxide film formed on the wafer 4 before the oxidation treatment step is determined by the exposure time for which the wafers 4 are exposed to oxygen atmosphere in the furnace tube 2, the oxygen concentration in the furnace tube 2, the temperature in the furnace tube 2, etc.
Here, with respect to the conventional diffusion furnace, since oxygen atmospheric layer has been formed entirely in the furnace tube 2 when the wafers 4 are introduced into the furnace tube 2, wafers located at the top and bottom sides of the wafer support boat 3 are exposed to oxygen atmosphere for different times, respectively (that is, the exposure time is different between the wafer located at the top side and the wafer located at the bottom side). Accordingly, the thickness of the oxide film formed before the oxidation treatment step is larger at the top side than at the bottom side, so that the in-batch film thickness uniformity is lowered.
The present invention has been implemented in view of the foregoing problem, and has an object to a semiconductor device manufacturing apparatus and a semiconductor device manufacturing method which can form an oxide film uniformly in a batch of wafer when the oxide film is formed on a wafer mounted in each part of a wafer support boat which is inserted in a furnace tube.
In order to attain the above object, according to a semiconductor device manufacturing apparatus of the present invention, a furnace tube port gas introducing pipe (port) for supplying desired gas is provided at only one end of the furnace tube, and when a treating target of semiconductor wafer such as silicon wafer is put into the furnace tube, an atmospheric layer of one or more kinds of desired gas is formed only at the port of the furnace tube by the desired reactive gas such as oxidative gas supplied from the furnace tube port gas introducing pipe. More specifically, the semiconductor device manufacturing apparatus of the present invention has the following feature.
According to one aspect of the present invention, a member to be treated or treating target is inserted into the furnace tube from one end of the furnace tube, and when the member to be treated is inserted, gas containing at least reactive gas is introduced into the furnace tube from a gas introducing port disposed near to the one end of the furnace tube to thereby supply the gas to the member to be treated while gas containing at least non-reactive gas is supplied into the furnace tube from another gas introducing port.
Further, according to the present invention, in a semiconductor device manufacturing method using a semiconductor device manufacturing apparatus in which a batch of plural semiconductor substrates serving as treatment targets are inserted into a furnace tube to perform the treatment such as oxidation on the substrates, in a process of inserting the batch of the plural semiconductor substrates serving as the treatment targets from an insertion port at one end of the furnace tube into the furnace tube, gas containing at least reactive gas is introduced into the furnace tube through a gas introducing port disposed near to the one end of the furnace tube in the direction substantially perpendicular to the batch insertion direction, thereby forming a gas atmosphere having a layer boundary in the direction substantially perpendicular to the batch insertion direction, and gas containing at least non-reactive gas is introduced through another gas introducing port of the furnace tube at the opposite end to the one end of the furnace tube, thereby making uniform in thickness the films formed on the plural substrates serving as the treatment targets under the gas atmosphere in the batch.
The present invention provides a semiconductor device manufacturing apparatus for performing a surface treatment of a semiconductor substrate, comprising:
a furnace tube having a port at one end thereof;
a heating means for the furnace tube;
a semiconductor substrate support means for inserting the semiconductor substrate into the furnace tube through the port of the furnace tube;
a first gas introducing port for introducing a reactive gas for the surface treatment into a first area of the inside of the furnace tube near to the port of the furnace tube; and
a second gas introducing port for introducing a non-reactive gas to the semiconductor substrate into a second area of the inside of the furnace tube at the other end side of the furnace tube, wherein the semiconductor substrate is moved to the second area by means of the semiconductor substrate support means.
The first gas introducing port may be disposed at a lateral surface of the furnace tube. The semiconductor substrate support means may support the semiconductor substrate perpendicularly to the insertion direction of the semiconductor substrate.
The first gas introducing port may have a first portion for introducing the reactive gas into the first area and a second portion for introducing a non-reactive gas to the semiconductor substrate into a third area of the inside of the furnace positioning the opposite side of the first area to the second area. The first gas introducing port may be divided into a plurality of divided portions relative to the insertion direction of the semiconductor substrate, and the reactive gas may be introduced into the first area through at least a part of the plurality of divided portions.
The second gas introducing port may be disposed at the other end of the furnace tube. The second gas introducing port may be also for use in introducing a reactive gas for the surface treatment.
The semiconductor substrate may be a silicon wafer, and the surface treatment may be an oxidation treatment of the surface of the silicon wafer. The reactive gas being introduced into the first area of the inside of the furnace tube from the first gas introducing port may be an oxygen gas diluted with one of a nitrogen gas and inert gas, and the non-reactive gas being introduced into the second area of the inside of the furnace tube from the second gas introducing port may be one of a nitrogen gas and inert gas.
The present invention also provides a method of manufacturing a semiconductor device for performing a surface treatment of a semiconductor substrate, wherein the following processes are simultaneously performed:
(a) a first process for inserting the semiconductor substrate at a fixed speed into a furnace tube through a port of the furnace tube at one end thereof;
(b) a second process for introducing a reactive gas for the surface treatment into a first area of the inside of the furnace tube near to the port of the furnace tube; and
(c) a third process for introducing a non-reactive gas to the semiconductor substrate into a second area of the inside of the furnace tube at the other end side of the furnace tube, wherein the semiconductor substrate is moved to the second area in the first process.
A reactive gas for the surface treatment may be introduced into the second area of the inside of the furnace tube after the semiconductor substrate is moved to the second area.
According to the present invention, the following effects can be obtained.
A first effect according to the present invention resides in that the thickness of the film formed under the gas atmosphere can be made uniform in batch of the wafers. The reason is as follows.
When the wafers are inserted into the furnace tube, the thickness of the film formed on each wafer is determined by the exposure time of the wafer to the gas atmosphere in the furnace tube if the other conditions are fixed. Therefore, according to the present invention, the gas atmospheric layer is formed only in the furnace tube port while the inert gas is filled in the furnace tube process portion, whereby no film is formed in the furnace tube process portion until the wafers are completely inserted into the furnace tube.
Accordingly, if the insertion speed of the wafer support boat into the furnace tube is kept constant, the passing time of the wafers through the gas atmospheric layer at the furnace tube port is equal both at the top side and at the bottom side of the batch of the wafers, and the films can be formed to have a uniform thickness in the batch.
A second effect of the present invention resides in that the thickness of the film formed under the gas atmosphere can be easily varied. The reason is as follows.
When the wafers are inserted into the furnace tube, the thickness of the films formed is determined by the width of the film forming gas atmospheric layer in the furnace tube port if the other conditions are fixed. Therefore, according to the present invention, the furnace tube port gas introducing pipe can be separated into plural parts, and the width of the gas atmospheric layer can be varied by selecting the boundary position between the parts of the furnace tube port gas introducing pipes to be used for forming the film forming gas atmospheric layer and not to be used therefor.